Millions of working parents will be entitled to unpaid parental leave this summer following new rules, it has been estimated.
The TUC said parents with at least one year's service with an employer qualify for 18 weeks of leave per child after new rules were introduced earlier this year.
General secretary Frances O'Grady said: "Many parents face huge difficulties combining work with childcare during the school holidays.
"Many will be using paid annual leave to spend time with their children. But with school holidays lasting around 13 weeks and workers entitled to less than six weeks' paid holiday a year, working parents need more support.
"Our message to employers is to be as supportive as they can when their staff request parental leave or need changes in their working hours over the summer holidays."